Resistor and high-frequency furnace



1,551,766 la.l F. NoRTHRUP Filed sept. so, 1922 5 sheets-sheet 1 Sept. l,` 1925.

RasIsToR AND HIGH FREQUENCY FURNACE M ra@ sept. 1, 1925.

1,551,766 E, F. NORTHRUP RESISTOR AND HIGH FREQUENCY FURNACE Filed Sept. 30. 1922 3 Sheets-Sheet 2 Sept. l; 1925.

E. F. NORTHRUP.

1RESISTOR AND HIGH FREQUENCY FURNACE 3 Sheets-Sheet 3 Filed Sept. 30, 1922 Patented Sept. l, 1925.

UNITED STATES PATENT oFEl'cE.

EDWIN F. NORTHRUP, OF PRINCETON, NEW JERSEY, ASSIGNOR T0 AJAX EIVECTRO- THERMIC CORPORATION, OF TRENTON, NEW JERSEY,` A CORPORATION OF NEW JERSEY.

RESISTOR AND HIGH-FREQUENCY FUBNACE.

Application led September 30, 1922. Serial No. 591,524.

T o all 'whom it may concern.'

Be it known that I, EDWIN F. NORTHRUP, a. citizen of the United States, residing at Princeton, in the county of Mercer and State of New Jersey, have invented a certain new and useful Resistor and High-Frequency Furnace, of which the following is a speciication. My invention relates primarily to furnaces having a resistor within the body of the furnace, and secondarily t'o a resistor type of furnace capable of acting also inductively.

lThe main' purpose of my invention -is to supply a spira'l resistor element preferably of graphite-carborundum mixture but permissibly of graphite or carbon or even noncarbonaceous material having its turns insulated electricallyfrom each other and from the melt, and in which the insulation from the melt is a good conductor of heat.

A further purpose is to provide a resistor spiral surrounding an electrically insulating but heat conducting crucible and seal the spiral outwardly by electrical and heat insulating materials so as to develop the full heat of the resistor within the metal.

A further purpose is to provide improved automatic connections so that the furnace can he lifted from its place of use for pouring purposes, at the same time breaking the current supply circuit and in which the circuit will again be closed when the furnace is reset.

A further purpose is to support the turns of the resistor against each other by material extending from one turn to the other preferably comprising a web and most desirably located at the inner circumference of the cylinder. This may remain in place during use or may be removed before the furnace is started, as preferred.

A further purpose is to improve the construction and insulation of the furnace.

A further purpose is to supply a furnace `adapted for resistor furnace uses at low frequency and for induction furnace purposes at high frequency.

A- further purpose is ,to prevent circulation of air up through and about the resistor which would cause oxidation of a resistor of oxidizable material such as gra hite.

A further purpose is to provi e a high frequenc furnace .having a carbonaceous and pre erably 'graphite-carborundum coil.

Further purposes will appear in the specification and in the claims.

I have preferred to illustrate my invention by one form only, selecting a form which in use has roved to be practical, effective and reliab e and which at the same time well illustrates the principles of my invention.

Figure 1 is a central vertical section of a furnace embodying my invention, corresponding to line 1-1 in Figure 2.

Figure l is a section corresponding to the rectangle 1-1 in Figure land upon an enlarged scale.

Figure 1b is a fragmentary section of Figure 2 upon line 1"---1b and upon an enlarged scale. l

Figure-2 is a top plan view of the furnace seen in Figure 1.

Figure 3 is a fragmentary vertical section showing a part of the furnace rim.

Figure 4 is a diagrammatic showing of one set of connections for high frequency use.

Figure 5 is a vertical section artly in elevation showing a resistor embodJying my invention.

Figure 6 is a section corresponding generally to the rectangle 1?- 8 of Figure 1 but showing a modified form.

In the drawings similar numerals indicate like parts.

My invention is capable of use for either of two quite different urposes.

It may be used with direct current or with relatively low frequency alternating current as a resistance furnace alone or, it may be used as an induction furnace when connected with a high frequency source of current and when suitable power factor-correction is made. l

When used as a. resistance furnace the C2R heat loss from the resistor is utilized within the furnace and is transmitted by conduction, convection and radiation to the charge. When used for an induction furnace, high frequency current is supplied from any suitable source, and corrected as to power factor by suitable means, passing the current through the spiral element as an induction coil. In this use the heatin is due partl to C2R heat in the resistor an partly to in uction on the charge.

I show one diagrammatic form of connections only but recognize that many other forms of high fre uency connection may be made, some of which are illustrated in my Patents Nos. 1,286,394, 1,286,395, 1,297,393 and 1,330,133.

Describing the form shown in illustration and not in limitation The body terminates in an electrically conductive base 5, conical in form and making good contact throughsprings 6 with an electrically conductive conical support 7 in which the base rests. The springs lie in grooves y8 and are held in position in any way, such as by being bent over the edge of the support and riveted at 7.

The resistance element is preferably of a graphite-carborundum composition with a inder compressed under considerable pressure but may be of graphite alone or of a form of carbon such as gas carbon for example. Even mineral substances with a binder would serve the purpose suiting the resistance to the conditions of design so that the (12R loss in the resistance at the vol-- tage available shall Vequal the required needs for the furnace.

The resistor is in the form of a helical spiral 9 closed at the bottom at 1() and terminating at the top in a ring -11 where it is encircled by a split cap 12, carrying the pouring spout 13. The cap is held in position by-bolts 14 passing through ears 15.

The spacing between the individual turns of the resistor at 16 and the spacing at 17 about the resistor are filled with an electrically insulating paste material which hardens in place and is then baked. Where a separate Crucible is used inside the resistor the paste material may be used as at 17 to coat the interior of the resistor so as to protect the resistor from the air, but it should be a better heat conductor than the other. The resistor is thus incased in the paste insulating material which is also a heat insulator and which maybe a combination of asbestos with a clay binder, or chrome with a binder. It is low in heat conductivity and electrical conductivity because of excess of binder. There are several materials on the market among which to choose for this purpose, known in the trade as zirkite, bauxite and alundum.

I leave room at the top and bottom for the fiange 18 upon the cap and the flange 19 upon a preferably cast metal plate 20. This plate is provided with a depending threaded boss at the center at 21 and with the feet 22, all resting upon an insulating disc 23 beneath the furnace.

This insulator may be of alberene or electrobestos, for example, and is held in position by a clamping contact member 24 flanged at 25 to give support to the insulator and screwed at 26 into the boss 21.

The furnace body is surrounded by a preferably cylindrical insulator 27 which ma also be of alberene or electrobestos, an the plate 20 is flanged as at 20 to close the annular space between the insulator 17 and the insulator 27. I line this annular space with a mica bushing 28 and fill it with a fine granulated insulating material 28', for which purpose I have found lampblack suitable, preferably mixing it with silica.

The interior of the resistor should be protected by electrically insulating material which is high in heat conductivity.

I prefer to use a crulcible 29 which is separate and distinct from the paste lining and which may be of any vone of a varietyof existing Crucible materials but for which a graphite-carborundum-binder composition would also be suitable. Graphite or carborundum or chrome with a clay binder would be suitable. A very satisfactory Crucible of material known as Tercod is on the market comprising graphite, carborundum and a binder and various patentees have indicated compositions intended for crucibles among them Ohman, No. 1,356,939. The Crucible should fit as close as may be convenient and should be sealed in at the top with some such material as thermolith. A supplemental bottom 30 may be used. The use of such a material as a resistor element is new to me and is claimed by me in a separate application.

Where it is desired to build in a lining 29 as a paste', a `lchrome-anol-binder such as thermolith or a graphite-carborundum binder composition such as disclosed in the Ohman Patent No. 1,356,939, may be used. The materials used between and outside the resistor turns and as a paste would be good as electrical insulators and :1s-protecting from the air but are not good enough heat conductors to get the best results.

As the resistor element is preferably of fragile material and there is danger of breakage during transportation, I support one turn from the next so as to prevent longitudinal movement and stiii'en the entire element lengthwise and transverselv against both axial and radial strains. It is desirable that the turns be supported at intervals at a number of points about-each turn and the most thorough means of securing this is by continuous web support shown at 9 on the drawing. The web may be small enough to offer but little short circuit to the path of the current about the spiral, in which case it may be left in place when the furnace is installed. On the other hand, being thin, it can be broken out readily to leave the resistor in the form shown in 'Figure 1 Where it is intended to allow the supporting web to remain it is desirable to put it at the inside of the support rather than further away from the -center because the smaller diameter of the web means a smaller path of current travel across it. i

The resistpr and its insulation lare enclosed within a metallic shell or casing 31 secured to the conical base 5 and connected with the insulation 23 by a ring spacer 32.

To the top of the casino' 31 is secured an electrically conductive r1ng 33 which is maintained in electrical connection. with the flange 34 of the top or cap by means of electrically conductlng contact fingers 35 which are spring pressed to improve their electrical contact by spiral springs 36 about bolts 37.

The furnace as thus described is adapted to be lifted bodily by any suitable crane and bearing members engaging the trunnions 38, so that the furnace may thus be turned upon the trunnions to pour, orthe furnace may be rested in outside bearings for the pouring operation.

The support 7 is interiorly flanged at 40 and the flange is apertured at 40. The flange supports an insulating disc 41 which may be of alberene or electrobestos. apertured at 42 so as to allow passage of a stud 43 depending from ya contact plate 44. The plate may be rested upon or otherwise secured to the insulating disc 41.

The lower end of the stud 43 carries a binding post 45 for one of the electrical connections. The other electrical connection may be made to any part of the support 7 as by binding post 46.

It will be noted that the electrical circuit is complete from the binding post 46, through support 7, springs 6, which flatten out to give good contact with base 5, through casing 31 springs 35 and cap l2 to the upper end of the resistor, and from the bottom of resistor through plate 20 and contacts 24 and 44, to binding post 45.

F or resistance furnace uses, a large current of low voltage may be used, either direct or alternating current of commercial frcquency.

,Vhere the intention, however, is to use the furnace as an induction furnace the current must be alternating current of fairly high frequency, much higher than the commercial frequencies in use for induction fur- `naces having inter-linkage of transformer iron. The frequency should preferably not be less than four hundred and eighty and desirably may be very much higher.

- In Figure 4 I have shown one series of connections diagrammatically for the urpose merely'of indicating some connections which may be used to supply high frequency current to the spiral conductor.

It is is connected to the extremities of the coil i. e., to the binding posts 45 and 46, b conductors 48 and 49 across which is bri ged a condenser 50.`- A reactance 51 may be used in series and the condenser or the reactance or both may be made adjustable to secure the best results, tuning as in my Patent No. 1,286,394 is desired.

Obviously the structure of Figure 1 could be applied to furnaces revoluble about the axis of the yfurnaces or oscillated thereabout, giving extra spacing of the resistor turns adjacent the inlet-outlet and closing the ends of the furnace.

It will be obvious that my disclosure here will suggest to others skilled in the art many ways in which the present invention may be practiced both for the resistance and for induction furnace uses and it is my intention to include all such as come within the reasonable spirit and scope of my invention.

Having thus Ydescribed my invention what I claim as new and desire to secure by Letters Patent is 1. In a resistance furnace, a resistor element comprising a hollow cylindrical nonmetallic member having a spiral groove starting at a distance from the top so as to leave a continuous cylindrical surface at the top, extending substantially to the bottom of the hollow portion and which is closed at one endl against air circulation axially of the resistor and an insulating lining for the hollow of the cylindrical member.

2. In a resistance furnace, a resistor element comprising a hollow cylindrical nonmetallic member having a spiral groovle starting at a distance from the top so as to leave a continuous cylindrical surface at the top and extending substantially to the bottom of the hollow portion and having a solid bottom and an insulating lining for the hollow of the cylindrical member.

3. In a resistance furnace, a hollow spiral resistor element of general cylindrical form having a closed bottom `and insulation between the turns of and within the spiral.

4. In an electric furnace, a spiral conductor embedded in electrical insulation having relatively poor conductivity for heat in combination with interior electrical insulation for the conductor having a relatively high conductivity for heat, a cap for one end o f the spiral conductor, a base for the `other end of the spiral conductor and rigid therewith and connections for conveysulation between the turns of the conductor, a cap for the conductor to which one electric terminal is connected and a base for the conductor to which the other terminal is adapted to be connected.

6. In an electric furnace, a combined resistance and high frequency furnace element comprising a spiraled graphite-carborundum conductor, a crucible having relatively high heat conductivity andrelatively low electrical conductivity inside the spiralled conductor, insulation between the turns of the conductor, a cap for the conductor to which one electric terminal is connected and a base for the conductor integral with and forming a bottom for the spiral, to which the other terminal is adapted to be connected.

7. In an electric furnace, a hollow resistor comprising a spiral of graphite and carborundum mixed and united by a binder.

8. In an electric furnace, a hollow resistor comprising a spiral containing carborundum intimately encased in in insulator.

9. In an electric furnace, a spiral resistor having an integral bottom in combination with a clamp for the top of the resistor, connections for passing electric current from the top to the bottom through the resistor and a filling for the space between the adjacent turns merging into a lining within the turns.

10. In an electric furnace, a spiral resistor, a clamp engaging the resistor at the top and adapted to receive an electric current in combination with means for completing electric circuit through the lower end of the resistor and insulation between the turns of and cylindrically within the resistor.

11. In an electric furnace, an electrically conducting cap, a non-metallic electrically conducting spiral resistor connected therewith, a bottom plate making electrical contact with the spiral, electrical insulation having good heat conductivity inside of said resistor and electrical insulation having poor heat conductivity between the turns of the spiral.

12. In an electric furnace, an electrically conducting cap, a non-metallic electrically conducting spiral resistor connected therewith, having a solid bottom, insulation for the resistor between its turns and within it and connections for supplying current to the top and bottom.

13. An electric furnace comprising a spiraled non-metallic resistor, electrical insulation having low heat conductivity between the turns of the spiral and outside of the resistor, electrical insulation having high heat conductivity inside of said spiral and rigidly joined to the first insulation and top and bottom connections for assing electric current through from one en of the resistor to the other.

14. An electric furnace comprising a spiraled non-metallic resistor, electrical'insulation having low heat conductivity between the turns of the spiral and outside of the resistor, electrical insulation having high heat conductivity inside of said spiral and comprising a crucible separate therefrom and top and bottom connections for passing electric current through from one end of the resistor to the other.

15. An electric furnace comprising a spiraled non-metallic resistor, electrical insulation having low heat conductivity between the turns of the spiral and outside of the resistor, electrical insulation having high heat conductivity inside of said spiral and made up of a protective lining following the contour of the resistor, a crucible separate from the lining and inside it and top and bottom connections for passing electric current through from one end of the resistor to the other.

16. An electric furnace comprising a spiraled non-metallic resistor, electrical insulation having low heat conductivity between the turns of the spiral and outside of the resistor, electrical insulation having high heat conductivity inside of said spiral and made up of a protective lining following the contour of the resistor, a crucible separate from the lining and inside it, sealing material holding the crucible rigid with respect to the resistor and top and bottom connections for passing electric current through from one end of the resistor to the other.

17. In an electric furnace, an electrically conducting cap, a non-metallic electrically conducting spiral resistor connected therewith, a bottom plate making electrical contact with the spiral, electrical insulation having good heat conductivity inside of said resistor, Aa contact piece connected with the bottom plate, a tapered contact piece connected with the casing and cooperating con-I tacts adapted to engage with the two contact pieces automatically as the furnace is seated in position.

18. In an electric furnace, an electrically conducting cap, a non-metallic electrically conducting spiral resistor connected therewith having a solid bottom, a bottom plate making electrical contact therewith, electrical insulation having good lheat conductivity inside of said resistor', a contact piece connected with the bottom plate, a tapered contact piece connected with the casing and cooperating contacts adapted to engage with the two contact pieces automatically as the furnace is seated in position.

19. In an electric furnace, an outer casing, a tapered contact secured to the bottom of the casing, a cap electrically connected with the casing, a spiral conductor connected with the cap, a second contact connected with the bottom of the spiraled conductor and located within the* said tapered contact and cooperating fixed contacts adapted to be engaged by the tapered contact and second contact respectively, when the furnace is seated in position.

20. In an electric furnace, a spiral conductor, a crucible withinw the conductor, a contact beneath the crucible connected with the lower part of the conductor, an electrically conducting casing about the conductor, connections between it and the conductor, a frustro-conical contact connected to the casing and Surrounding the first contact and coo erating contacts automaticallyengaged by t e contacts o f the furnace when the furnace is seated in position.

21. A portable. electric furnace having a conical contact and a contact interior to the cone represented by the first contact, in combination with a contact cooperating with the interior contact to take the greater part of the weight of the furnace, a steadying conical contact and springs between the conical contacts to ensure good conductivity independently of the accuracy of fit of the cones'.

22. A portable electric furnace and stand therefor having cooperating conical contacts and cooperating contacts interior thereto taking the greater part of the weight of the furnace, and springs lying within rooves in one of the conical contacts an yieldingly engaging the other conical contact.

23. A portable electric furnace and stand therefor having cooperating conical con-` tacts and cooperating contacts interior thereto taking the greater part of the wei ht of the furnace and springs lying wit in grooves in one ofthe conical contacts pressing against said conical contact at both ends and yleldingly engaging theother conical contact at the intermediate parts of the lengths of the springs.

24. In. an electric furnace, a non-metallic spiraled electrical conductor, in combination with insulating material about the conductor inside, between and outside the turns -of the spiral, rigidly connected with the spiral, the insulation inside the spiral havlng higher heat conductivity than-that between the turns and outside of the spiral,-

assing electric curand connections for rent through said con uctor.

25. In en electric furnace, a spiral conductor embedded in insulation having one heat conductivity inside the conductorand havmg a different conductivity outside the conductor and connections for passing electric current-throu h the conductor. j

26. I n an e ectric furnace, a graphite or carbon resistor elemen vconsists in forming t `port between .the turns of very small relat, insulation having poor lconductivity between the turns of the element, insulation having high heat conductivity radially inside of the turns asa lining, a crucible within the\ spiral element and -connections for passing electric current through lthe element.

27. In an electric furnace, a carbonaceous -port them mechanical y.

29. In la resistance furnace, a non-metalh'c spiral resistor furnace having a web of material following the contour of the spirals between them to support the spiral portion mechanically. Y

'30. In aresistance furnace, a spiral resistor element havin integral support from one spiral turn to t e next adjacent turn to support one from the other.

3l. In a `resistance furnace, a hollow iral resistor element of general cylindrical orm having a closed bottom and having the interior of the spiral integrally closed at the bottom of the groove and at the top of the element terminating short of the end of the cylinder.

32. In a resistance furnace, a resistor element comprising a cylinder separated into spiral sections by a groove extending part wa only through the thickness of the cylin er -to leave a web of supporting matenal between.

33. In a resistance furnace, a resistor element comprising a graphite-carborundum cylinder c osed at one end and having a groove in the cylinder startin at' a point near the open end and exten ing throu h the greater part but not wholl throu h the sov cylinder, leaving a portion 'o the cy inder .as a fstifener between the spiral turns.

-85. he process of protectingja spir resister furnace element from breakage durincg handling and of prepperig it io; :vhip

lll

tive section and removing this support when the resistor is put inservice. 

